https://www.snmclub.com/ by Dalal Alqahtani‏

1. Factors Affecting the Biodistribution of
Radiopharmaceuticals

3.  Describe examples of altered radiopharmaceutical biodistribution related
to improper product preparation.
Upon successful completion of this lesson, the reader should be able to:

4. PrinciplesofNuclearMedicine

5. Radiopharmaceuticals
Defined as radioactive drugs that, when used for the purpose of diagnosis or
therapy, typically elicit no physiological response from the patient.

6. Nuclear pharmacists must understand how radiopharmaceuticals work; i.e., their
mechanism of action. Such knowledge is necessary to understand the performance of
clinical nuclear medicine procedures, many drug-radiopharmaceutical interactions, and
other causes of altered biodistribution.

7. Improve your critical thinking
with nuclear medicine cases.

8. Factors Affecting the Biodistribution of Radiopharmaceuticals
1
• Factors associated with radiopharmaceutical
preparation and formulation .
2
• Factors caused by radiopharmaceutical
administration techniques and procedures .
3
• Factors caused by pathophysiological and
biochemical changes .
4
• Factors caused by medical procedures.

9. It is important to recognize these factors and to understand the specific
mechanisms involved in the altered biodistribution to avoid bot
h false-positive and false negative interpretation of scans.

10. Factors associated with radiopharmaceutical
preparation and formulation.

11. Altered biodistribution of 99mTc-MDP bone scan caused by radiochemical impurities.
(A) Thyroid uptake caused by free 99mTc pertechnetate. (B) Diffuse liver uptake cause
d by 99mTc colloids.

12. o Radiochemical purity (RCP) may be defined as "the proportion of the total
radioactivity in the sample which is present as the desired radiolabelled species.
o Radiochemical purity is important , since it is the radiochemical form which
determines the biodistribution of the radiopharmaceutical.
o Radiochemical impurities will have different patterns of biodistribution which may
obscure the diagnostic image obtained and render the investgation meaningless.
Radiochemical purities.

14. Factors caused by radiopharmaceutical
administration techniques and procedures.

15. Infiltrated Injection.
Most defects related to radiopharmaceutical
administration are the result of extravascular or
infiltrated activity at the injection site.

16. Formation of Blood Clots in the Syringe. While radiopharmaceuticals are being
injected intravenously, during back withdrawal of unanticoagulated blood into the
syringe, blood clots may form. The radiopharmaceutical could then bind to clots and
localize in the lung.

17. Lung scan showing blood clots. During intraveno
us administration of 99mTc-MAA, blood was first
withdrawn into the syringe and labeled clots were
subsequently reinjected.

18. Patient Position During Radiopharmaceutical Administration. Decreased activity
in the upper lobes of the lung perfusion scan with the use of either 99mTc-MAA
or 99mTc-DTPA radioaerosol has been observed when the patient was sitting at the
time of dose administration.

19. Lung perfusion scan with 99mTc-MAA. (A) Hypoperfusion of
upper lobes when the patient was sitting at the time of injection.
(B) Repeat scan on the next day shows normal perfusion while
the patient was supine during the injection.

20. (A) Normal uptake of Tc-99m pertechnetate in thyroid (and salivary glands).
(B) Absent thyroid uptake (arrow) of Tc-99m pertechnetate in a patient who was administered
iodinated x-ray contrast media a few days before.

21. Factors caused by pathophysiological and
biochemical changes .

22. Effect of sudden increase in insulin levels on FDG-PET. In a patient undergoing
staging of lymphoma, the FDG-PET scan was performed after the patient had ea
ten a candy bar 30 minutes before FDG injection.

23. Delayed tracer excretion in hydronephrotic right kidney.

24. Brown fat activity
intense FDG activity in the bilateral
neck and paravertebral regions with
a symmetrical distribution.

25. Brown fat activity is seen more commonly in younger patients and is also increased in
response to hypothermia (so keep patients warm both pre and post injection of FDG).

26. Factors caused by medical procedures.

27. The biodistribution of radiopharmaceuticals may also be altered
significantly because of medical procedures, such as radiation therapy
surgery, and hemodialysis. 9mTc-MDP bone scan demonstrating decreased
thoracic spine uptake due to prior radiation therapy.

28. References
https://pharmacyce.unm.edu/nuclear_program/freelessonfiles/Vol16Lesson4.pdf
https://www.radiochemistry.org/nuclearmedicine/radiopharm_define.shtml
https://cardiologydoc.wordpress.com/2012/01/30/brown-fat-and-obesity/
https://medapparatus.com/NuclearMedicine/NuclearMedicine_Page4.html

29. Dalal Mnis Al-Qahtani
Nuclear medicine specialist